Ideally, you'd be looking at Pages, Numbers or Keynote which are the Apple versions of MS Office products, but costing a lot less money, and they're also compatible with their MS Office counterparts.
I use Documents to Go and find that it works quite well. Others prefer Apple's Pages and Numbers.
There's no shortage of apps, things you need to watch out for is if they are cloud based, which can mean they don't work if you're not online. Also something to consider, most if not all apps are skinnied down from their original programs, so while they certainly have basic function, they won't have all the bells and whistles of the original programs. (Usually you can type and the such, just limited on fancy formatting)